A surgery assisting apparatus for controlling a posture of a first surgical tool to be inserted into a body cavity and mechanically driven, by using a second surgical tool to be inserted into the body cavity, comprises: a mode switch configured to switch a first mode and a second mode, the second surgical tool being used to control the first surgical tool in the second mode； one or more sensors configured to measure an angle and depth of insertion of a shaft of the second surgical tool into the body cavity； and at least one memory and at least one processor which function as a computing unit configured to determine a target position of a control point that is a point for specifying the posture of the first surgical tool in order to control the posture of the first surgical tool.
